all the things are done on centos 6.3 but steps should be same for any Linux system.
1) Installing EPEL repoSince centos repo doesn't contain the vpnc, we need to configure additional repo call EPEL.
It is straightforward installation and document can be found form here.
Please find "How can I install the packages from the EPEL software repository? " from content and install it. you may need to enable EPEL repo sometime.
2) Installing vpnconce you enabled the rpmforge repo, type following command to install vpnc
[root@localhost ~]#yum install vpnc
3)Chang folder permissionI installed the vpnc as root.if you wish to run vpnc as normal user other than root .change file permission of vpnc installaion directory
4)Download pcf2vpnc[root@localhost ~]#wget http://svn.unix-ag.uni-kl.de/vpnc/trunk/pcf2vpnc
5)Convert pcf file[root@localhost ~]#perl pcf2vpnc demopcf.pcf demovpnc.conf
change ownership of *.conf file if you need
6)copy *.conf to /etc/vpnc/[root@localhost ~]#cp demovpnc.conf /etc/vpnc/
7)Start vpnc[root@localhost ~]#vpnc demovpnc
Enter password for user@A.B.C.D:
(A.B.C.D is public ip address where you need to connect, user is username , you need to enter password )